1. Field of the Invention
This invention pertains generally to cardiovascular implants, and more particularly to devices that completely replace a failing heart to provide blood flow to the pulmonary and systemic circulation.
2. Description of Related Art
Congestive heart failure is a major, rapidly growing public health problem that results in hundreds of thousands of deaths annually. Patients with bi-ventricular end stage heart failure who are refractory to medications, surgical intervention and resynchronizer pacing are best treated with cardiac transplantation. However, donor hearts are limited to about 2,000 per year in the United States and, consequently, there is a large unmet need for approximately 75,000 patients who would benefit from cardiac transplantation, but for whom no donor heart is available. A mechanical total artificial heart (TAH) could replace a failing heart and offer improved survival and functional capability comparable to cardiac transplantation.
Extensive research since the mid 1960's has resulted in numerous left ventricular assist devices (LVAD) intended to take over part or all of the work of the left ventricle while working in parallel with the native heart. The HeartMate™, is a positive displacement pump used as a bridge to cardiac transplantation and destination therapy in patients with severe congestive heart failure. Most recently, the HeartMate™ II, a rotary pump, has received PMA approval for bridge to transplantation. LVAD's such as these are gaining clinical acceptance, but development of total artificial hearts (TAH) has not kept pace, particularly for permanent assistance without intention to bridge to cardiac transplantation. Two total artificial hearts are clinically available on a very limited basis in the United States.
The SynCardia TAH by CardioWest is implanted in the chest and is powered by an external pneumatic driver via air hoses which penetrate the chest. It has been approved for temporary use as a bridge to transplantation in patients who cannot be supported with an LVAD alone and has demonstrated clinical efficacy in several hundred patients. The Abiocor™ TAH by Abiomed, Inc. is intended for permanent use and is totally implantable. It has a self-contained electric motor and receives power by means of transcutaneous power transmission, but has been approved by FDA only for compassionate use.
Each of the CardioWest and Abiocor devices employ two separate pumps to replace the right and left ventricles, respectively. These pumps are positive displacement pumps with two valves per pump (total of four valves) to ensure unidirectional flow of blood. The anatomical compatibility of these devices has limited their use to larger patients, since positive displacement pumps are inherently large.
Rotary blood pumps based on centrifugal or axial flow hydraulics have proven to be safe and durable pumps for use as left ventricular devices and could offer many advantages over positive displacement pumps if they were adapted for use as a total artificial heart. Most importantly, rotary blood pumps would be much smaller than existing pulsatile TAH's and would not require artificial valves or a means for volume compensation or venting. In addition, rotary blood pumps, such as the HeartMate II, have proven durability for many years.
To date, all total artificial hearts employ two pumps whether they are positive displacement type or rotary pumps. All of the TAH's based on rotary blood pumps integrate the right and left heart pumps into a single housing which is an improvement over the use of two separate pumps.
A total artificial heart based on a single rotary impeller would offer significant advantage in reduced size, simplicity and cost over existing devices intended for complete replacement of the heart.